Stage I of tail regeneration. Eublepharis macularius. (A,B) Gross morphology of the autotomy surface in caudal (A) and dorsal view (B). Integument begins to collapse/retract and various skeletal and non-skeletal tissues are observed to protrude. Recesses for projecting muscle processes from the autotomized tail are indicated (white asterisks). Note the caudal artery (circle). (C) Gross morphology of the autotomized portion of the tail in cranial view. Position of the caudal artery indicated (circle). Note the star-like pattern formed by projecting muscle processes. (D-F) Serial sections stained with Masson's trichrome (dorsal towards top of page). (D) Sagittal section of tail, (autotomy surface to right). Collapsed recess for projecting muscle process indicated (black asterisk). The spinal cord (stained pink) is centrally positioned. Ventral and parallel to the spinal cord is the notochord (in this view stained red with green mottles) and intervertebral disc (stained green). Surrounding the skeletal are bands of adipose tissue (unstained) and skeletal muscle (stained red). Position of intravertebral fracture planes indicated (black arrows). (E) Closer view of the region identified in panel (D) taken from a different section. Note the developing clot (stained red and green) distal to the torn and retracted spinal cord (autotomy surface to right). (F) Transverse section through contracted sphincter of the caudal artery. at, adipose tissue; ca, caudal artery; cl, clot; ch, chevron; cv, caudal vein; de, dermis; em, epaxial musculature; hm, hypaxial musculature; no, notochord; nc, notochordal cartilage; ns, neural spine; sc, spinal cord; sp, arterial sphincter. Scale bars: d = 500 μm; e = 100 μm; f = 20 μm.